Method of extruding tubular products

ABSTRACT

A method is provided for extruding a tubular product wherein a billet is loaded into a container in a press, the billet is restrained in the container by crushing it between a ram and a die block, the die block is moved with respect to the billet so that the end of the billet toward the die block is substantially unrestricted, the billet is pierced with a mandrel, and the pierced billet is extruded over the mandrel and through the extrusion die.

United States Patent Livelsberger July 17, 1973 [54] METHOD OF EXTRUDINGTUBULAR 2,798,286 7/1957 Anderson 72/266 O CT 3,408,846 ll/l968Schofield 72/267 [75] inventor: Bert V. Llvelsberger, Mulberry, ind.Primary fixaminerncharles w Lanham [73] Assignee: Aluminum Company ofAmerica, istant Exam erR0bert M. Rogers v Pittsburgh, Pa, Attorney-DavidW. Brownlee 22 F1 d: A .25, 1971 l 1 57 ABSTRACT [21] Appl. N0.: 174,880A method is provided for extruding a tubular product wherein a billet isloaded into a container in a press, the [52] US. Cl. 72/265 billet isrestrained in the container by crushing it be- [51] Int. Cl. B2lc 23/20tween a m and a die block, the die block is m ved [58] Field of Search72/264, 254, 255, with pec t t e b e o that the end of the billet t0-72/256, 266, 265 ward the die block is substantially unrestricted, thebi]- let is pierced with a mandrel, and the pierced billet is [56]References Cited extruded over the mandrel and through the extrusion kUNITED STATES PATENTS l,948,242 2/ 1934 Schubarth 72/266 6 Claims, 5Drawing Figures 1 METHOD OF EXTRUDING TUBULAR PRODUCTS BACKGROUND OF THEINVENTION In extruding tubular products over a mandrel, it has beencommon practice to pierce a billet with the mandrel with the billetrestrained against an open extrusion die. In so piercing a billet, aslug of metal in the form of an extruded rod is pushed through the opendie by the piercing mandrel. In addition to the metal lost as a piercedplug, the'plug adheres to the tube that is subsequently extruded andprevents air from entering the tube as it is being extruded. The vacuumthat is produced may cause collapse of the extruded tube and can resultin scrapping of the collapsed tube. To avoid such collapse, the end ofthe extruded tube has sometimes been punctured or cut in order to permitair to enter the end of the tube.

Accordingly, a method of extruding a tubular product is desired whichwill not produce an extruded plug of material-on the endof the extrudedtubular member.

SUMMARY OF THE INVENTION This invention provides a method of extruding abillet over a mandrel and through an extrusion die to form a tubularproduct in whichduring piercing with the mandrel, the billet isrestrained in a container in the press without substantially restrictingdeformation of the material atthe die end of the billet. The billet ispierced against lateral restraint only whereby the forward end of thebillet can be formed around the nose of the mandrel during penetrationwithout producing a slug of metal. According to the invention, thelateral restraint of the billet in its container may be provided bycrushing the billet between a die block and a ram so that the billet islocked in the container by frictional and shear forcesatthebillet/container interface. The die block can then'be moved withrespect to the billet so that the forward end of the billet issubstantially unrestrained during piercing. v

Accordingly, an object of the invention is to provide an improved methodof extruding a tubular product.

Another object of the invention is to provide a methodof extruding atubular product over a mandrel in an extrusion die wherein, duringpiercing, a billet is laterally restrained in-its container withoutsubstantially'restricting the die end of the billet with tools.

A further object of the invention is to provide a method of extruding atubular product in which a billet is crushed in its container in a pressbetween a die block and a ram whereafter the die block is spaced fromthe forward end of the billet during piercing so that the mandrel canpierce the billet without extruding a slug of materialthrough the dieaperture.

A further object of the invention is to provide a method of extruding atubular product in which less force is required to pierce a billet thanis required by conventional methods.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects andadvantages of the invention will be more fully understood andappreciated with reference to the following description and the drawingsappended thereto wherein:

FIG. 1 is a fragmentary cross-sectional view of extrusion apparatus witha billet therein;

FIG. 2 is a fragmentary cross-sectional view similar to FIG. I with thebillet crushed in its container;

FIG. 3 is a fragmentary cross-sectional view similar to FIGS. 1 and 2showing the extrusion die spaced with respect to the billet;

FIG. 4 is a fragmentary cross-sectional view similar to FIGS. 1 3'showing piercing of the billet; and

FIG. 5 is a fragmentary cross-sectional view similar to FIGS. 1 4showing extrusion of a tubular product over the mandrel and through thedie aperture in the die.

DESCRIPTION OF A PREFERRED MODE Referring to the Figs, extrusionapparatus is shown which may be employed'in either direct or indirect(inverted) extrusion processes depending onthe press arrangement. Thedifference between direct and indirect extrusion is primarily a matterof whether there is relative movement between the container and ram(direct) or between the container and the die (indirect), and bothinclude the same basic apparatus. With respect to the invention, it isequally well suited to use in either direct or indirect extrusionpresses.

The apparatus which has been selected for illustration has been designedfor the extrusion of aluminum or an alloy thereof, but the invention canbe employed in the extrusion of many other materials such as lead,copper, brass, steel, or the like which are commonly extruded in tubularform. A preferred mode of the invention will be described with respectto. the extrusion of aluminum as being exemplary of the practice of theinvention.

FIG. 1 illustrates a typical press arrangement for extruding a tubularproduct including an extrusion die 10, an extrusion container 12, apressure ram 14 and a mandrel 16 with a nose or piercer l8 thereon. Aswill be explained, piercer 18 preferably has a low angle tip or needlenose thereon but may also have a blunt nose of various configurations asis well known for conventional extrusion processes. Extrusion die 10 hasa die aperture 20 therein which has dimensions approximating the outerdimensions of the tubular products to be extruded, and mandrel 16 has anextruding surface 22 which approximates the inside dimensions of theproduct to be extruded. In the apparatus selected for illustration,mandrel 16 does not move with respect to die aperture 20 duringextrusion, although the mandrel may also be advanced through the dieaperture in the extrusion die during extrusion as is well known inconventional extrusion processes. It will also be obvious to thoseskilled in the art that a mandrel can be provided which has a pluralityof extrusion surfaces of different diameters, and which can besequentially advanced and/or retracted with respect to the die apertureto extrude tubular products having differing wall thicknesses. In theapparatus selected for illustration, the end of mandrel I6 is advancedinto die aperture 20 and locked in position so that the product which isextruded thereover will have a substantially uniform wall thickness.

FIG. I further shows a billet 24 to be extruded, loosely positioned incontainer 12 as is conventional. Billet 24 may be'a cast ingot or may beformed from plate or other stock material. In extruding an aluminumbillet, the billet is preferably pre-heated to a temperature in therange of 600 F to l,000 F so that the aluminum can be extruded moreeasily.

After a billet has been loaded into a container, it must be pierced by amandrel so that the nose of the mandrel can be positioned in the dieaperture for extruding a tubular product thereover. According to priorpractices, billets have usually been restrained against either an opendie or a dummy die block during piercing. When a billet is piercedagainst an open die, a slug of metal may be forced through the dieaperture by the mandrel as it displaces metal during piercing. Whenpierced against a dummy die block which prevents the formation of aslug, substantially more power is required to force the mandrel throughthe billet, and the mandrel cannot completely pierce the billet.

It is a feature of this invention that billet 24 is restrained incontainer 12 during piercing without substantially restricting the endof the billet with an open die or dummy die block. According to thisinvention, billet 24 is crushed or upset between die and pressure ram14, to lock the billet in the container, and the die is then moved awayfrom the billet to pennit piercing without tool restraint against theend of the billet. It will be obvious to one skilled in the art that adummy die block, not shown, could be substituted for die 10 for crushingbillet 24 against ram 14. Crushing billet 24 between die 10 and ram 14effects radial expansion of the billet against the inner walls ofcontainer 12 and thereby locks the billet in the container. This lockingeffect is produced by the pressure of the billet against the inner wallof the container and will hold the billet against the piercing force aswill be described. Depending on whether the extrusion apparatus isdesigned for direct or indirect extrusion, crushing may be effected bymoving either the ram 14 or the die 10 with respect to container 12. Forexample, in an indirect extrusion operation, the container 12 and ram 14may be moved toward die 10 which is stationary to compress billet 24between the die and the ram. In a direct extrusion operation, thecontainer and die may be stationary and the ram is usually moved withrespect to container and toward the die to squeeze a billet between thedie and the ram.

After billet 24 is crushed in container 12, die 10 is moved with respectto billet 24 to provide a space therebetween so that the face of thebillet is substantially unrestricted by tools. In indirect extrusionapparatus, this space may be provided by moving container 12 and ram 14rearward away from die 10. If a dummy die block is used for the crushingoperation, the block may be completely removed from the press for thepiercing operation. It is important that adequate space be providedadjacent the forward face of the billet for it to be deformed outwardlyas the billet is pierced by mandrel l6. Depending upon the size of thebillet, the size of the mandrel and the material being pierced amongother factors, the amount of defonnation may vary substantially. As anexample, an eleven inch diameter billet which is 14 inches long andwhich is pierced by a 3 and inch diameter piercer mandrel should haveapproximately 4 to 6 inches of clearance between its face and die 10 fordeformation of the billet.

Although not essential to the practice of the invention, a space mayalso be provided between the rear face of billet 24 and pressure ram 14during piercing to provide room for back flow of the material in thebillet during piercing. This clearance can be provided by restrainingcontainer 12 and retracting ram 14 to provide an inch or more of spacebetween the billet and the end of ram 14.

FIG. 4 shows billet 24 as it is being pierced by mandrel 16 and piercer18 on the end of the mandrel to produce a hemispherical dome on theforward face of the billet with a hole through the end of the dome. Asillustrated, the piercing stroke is completed with the tip of piercer 18having penetrated the end of billet 24. If a hole is not formed in theface of billet 24, the end of the tubular product which is subsequentlyextruded may also not have a hole in it. In the absence of a hole in theend of the tubular product, a vacuum could be produced in the productduring extrusion and such a vacuum could cause collapse of the product.Depending upon the shape of the piercer nose, the diameter of thepiercer, the material, the temperature of the billet, and billet shapeamong other factors, the hemispherical dome may be of various shapes andsizes. With some piercers, particularly blunt nose piercers, a ring ofmaterial may be separated from the face of the billet and may result inscrap material. Accordingly, a needle nosed piercer may be preferred forthe practice of the invention for some applications because such apiercer may facilitate forming a hole in the end of a billet with aminimum of deformation of the billet.

It has been found that a piercer with a nose which is slightly longerthan the radius of the dome which is formed on the billet works well inthe practice of the invention. If the nose is substantially longer thanthe radius of the dome on the billet, the nose may be weak and may bebroken or may be too flexible to form a concentric hole in the billetand extrude a product with a uniform wall thickness. If the length ofthe nose is less than the radius of the dome on the billet, the largerdiameter base of the mandrel must be forced further through the billetin order to completely pierce the billet. This increases deformation ofthe billet and may cause separation of a ring or ball of material fromthe face of the billet. It has been found that a piercer nose with alength in the range of approximately 1.25 to l .75 times the radius ofthe piercer mandrel, depending on the material, temperature, and tubesizes, among other factors, works well in the practice of the invention,although is not limiting of the invention.

The hemispherical dome is a result of flow of material in the billetoutward and forward ahead of the piercer nose. Since the face of thebillet 24 is unrestrained by tools, there is no external resistance tosuch deformation. Further, since die 10 is spaced from the forward faceof billet 24, no material is forced through the open die aperture 20 andno slug of scrap material is formed on the end of the tubular productwhich is subsequently extruded. Moreover, since there is no externalresistance to such deformation, the force required to pierce a billet bythe method of the invention is substantially less than the force whichis required for piercing a billet against an open die or a dummy dieblock. It has been found that the invention reduces the force requiredfor piercing a billet by as much as 50% or more from the force requiredfor piercing a billet by conventional methods.

After billet 24 has been pierced, it is again compressed or crushedbetween die 10 and pressure ram 14, and material from the billet isextruded through die aperture 20 around piercer 18 on mandrel 16 to forma tubular product. Although recrushing billet 24 and the extrusion ofmaterial through the die aperture is usually one continuous operation,recrushing of the billet between die 10 and ram 14 is sometimesconsidered to be a separate step in the extrusion process prior toactual extrusion of material. To effect extrusion of a tubular product,it may also be necessary to either ad vance or withdraw mandrel l6 andpiercer 18 so that extrusion surface 22 on the piercer is properlylocated in die aperture. This positioning of the extrusion surface 22may be done prior to, concurrently with, or subsequent to the recrushingof billet 24 after the piercing operation and is not critical to theinvention.

Upon extrusion of material through die aperture 20, the first portion ofthe tubular products 26 may include a small length of scrap 28 as shownin FIG. 5. Scrap portion'28 will usually be relatively small, however,and will have an open end or hole 30 therein so that air can enter thetube and therefore avoids collapse of the tube due to a vacuum in thetube.

It is therefore seen that a method has been illustrated and describedfor extruding a tubular product which does not produce a slug of metalon the end of the product which must be scrapped and which can causecollapse of the tubular product. The method involves piercing of abillet without substantially restraining the die end of the billetwhereby material from the billet can flow outward and forward ahead ofthe piercing mandrel without resistance from the tools. Although apreferred mode has been described, it will be obvious to those skilledin the art that numerous variations can be made in the method withoutdeparting from the invention. Included in such variations are theprovision of various shapes for the piercer on the mandrel, the use ofdirect or indirect extrusion apparatus and variations in the means forrestraining a billet in a container.

What is claimed is:

1. In a method of extruding a tubular product over a mandrel and throughan extrusion die, the improvement comprising the steps of:

crushing a billet in a container in a press between an extrusion die anda pressure ram to lock the billet in the container;

moving the die with respect to the billet to provide a spacetherebetween for deformation of the forward end of the billet duringpiercing;

piercing the billet with a mandrel; and

extruding a tubular product over the mandrel in the extrusion die.

2. A method as set forth in claim 1 in which, after crushing, thepressure ram is moved with respect to the billet to provide a spacetherebetween for back flow of material in the billet during piercing.

3. A method as set forth in claim 1 in which an aluminum alloy billetwhich has been heated to a temperature in the range of 600 F 900 F isextruded.

4. A method as set forth in claim 1 in which the billet is recrushedbetween the die and the ram after it has been pierced.

5. A method as set forth in claim 1 in which the billet is pierced witha mandrel with a needle nose piercer thereon.

6. A method as set forth in claim 5 in which said needle nose has alength in the range of 1.25 to 1.75 times the radius of the mandrel.

1. In a method of extruding a tubular product over a mandrel and through an extrusion die, the improvement comprising the steps of: crushing a billet in a container in a press between an extrusion die and a pressure ram to lock the billet in the container; moving the die with respect to the billet to provide a space therebetween for deformation of the forward end of the billet during piercing; piercing the billet with a mandrel; and extruding a tubular product over the mandrel in the extrusion die.
 2. A method as set forth in claim 1 in which, after crushing, the pressure ram is moved with respect to the billet to provide a space therebetween for back flow of material in the billet during piercing.
 3. A method as set forth in claim 1 in which an aluminum alloy billet which has been heated to a temperature in the range of 600* F - 900* F is extruded.
 4. A method as set forth in claim 1 in which the billet is recrushed between the die and the ram after it has been pierced.
 5. A method as set forth in claim 1 in which the billet is pierced with a mandrel with a needle nose piercer thereon.
 6. A method as set forth in claim 5 in which said needle nose has a length in the range of 1.25 to 1.75 times the radius of the mandrel. 